As a woman born with Cerebral Palsy, I'm not just defined by my condition. I write stories about ponies with disabilities because that’s my own experiences.
It's one thing to create/throw already-established characters in a story of some kind. It's another thing to develop those characters, regardless of the situation they're in.
I am a brony from Massachusetts with Autism who enjoys MLP, Disney and writing!
"...as for the Why: beyond the obvious financial motivation, it's exceedingly simple... because I can."